An anisotropically conductive sheet is a sheet exhibiting conductivity only in its thickness-wise direction or having pressure-sensitive conductive conductor parts exhibiting conductivity only in the thickness-wise direction when they are pressed in the thickness-wise direction. As such anisotropically conductive sheets, there have been known those of various structures, such as those obtained by uniformly dispersing metal particles in an elastomer (see, for example, Patent Art. 1), those obtained by unevenly dispersing a conductive magnetic metal in an elastomer, thereby forming a great number of conductive path-forming parts each extending in a thickness-wise direction thereof and an insulating part for mutually insulating them (see, for example, Patent Art. 2) and those obtained by defining a difference in level between the surface of each conductive path-forming part and an insulating part (see, for example, Patent Art. 3).
In these anisotropically conductive sheets, conductive particles are contained in an insulating elastic polymeric substance in a state oriented so as to align in the thickness-wise direction, and each conductive path is formed by a chain of a great number of conductive particles.
Since such an anisotropically conductive sheet has such features that compact electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that soft connection becomes feasible with mechanical shock or strain absorbed therein, it is widely used as an anisotropically conductive connector for achieving electrical connection between circuit devices, for example, electrical connection between a printed circuit board and a leadless chip carrier, liquid crystal panel or the like, in fields of, for example, electronic computers, electronic digital clocks, electronic cameras and computer key boards.
Further, as a means for achieving electrical connection between electrodes to be inspected of a circuit device, which is an object of inspection, and electrodes for inspection formed on the front surface of a circuit board for inspection in electrical inspection of circuit devices such as printed circuit boards and semiconductor integrated circuits, an anisotropically conductive sheet is used in place of a probe member, in which a plurality of pin probes are arranged corresponding to the electrode to be inspected.
That, in which either the probe member or the anisotropically conductive sheet may be used, is known as an inspection apparatus for circuit devices. A circuit board for inspection in this inspection apparatus has inspection electrodes each having a special form. An examples thereof is illustrated in FIG. 13. The inspection electrodes 6 in this circuit board 5 for inspection each have a cocoon-shaped form and are arranged in accordance with a pattern corresponding to a pattern of the electrodes to be inspected in a state inclined at an angle of, for example, 45°.
However, the inspection apparatus having the circuit board for inspection, in which the inspection electrodes of such a special form have been formed has been proved to involve the following problems when electrical inspection of a circuit device having projected electrodes, such as BGA, is conducted by using the anisotropically conductive sheet.
As the anisotropically conductive sheet in the inspection apparatus of the circuit board, is used that having conductive path-forming parts each having a diameter equivalent to the diameter of an electrode to be inspected in that high conductivity is achieved. However, in the circuit board 5 for inspection illustrated in FIG. 13, a pitch of the inspection electrodes 6, i.e., a center distance between inspection electrodes 6 adjoining each other, is substantially equal to a pitch of the electrodes to be inspected, but a clearance between inspection electrodes 6 adjoining each other is considerably smaller than a clearance between the electrodes to be inspected. Therefore, it is extremely difficult to arrange the anisotropically conductive sheet on the circuit board 5 for inspection in such a manner that each of the conductive path-forming parts thereof is located on an inspection electrode 6 to be connected and come into no contact with inspection electrodes 6 adjoining the inspection electrode.
In addition, when an anisotropically conductive sheet having conductive path-forming parts small in diameter is used, it is necessary to make the thickness of the conductive path-forming parts of the anisotropically conductive sheet small for the purpose of achieving necessary conductivity. However, the anisotropically conductive sheet having the conductive path-forming parts small in the thickness thereof is low in irregularity-absorbing property, so that it is difficult to surely achieve electrical connection to electrodes to be inspected when a circuit board, which is an object of inspection, has projected electrodes great in a scatter of projected height.    Patent Art. 1: Japanese Patent Application Laid-Open No. 93393/1976;    Patent Art. 2: Japanese Patent Application Laid-Open No. 147772/1978;    Patent Art. 3: Japanese Patent Application Laid-Open No. 250906/1986.